Commit message: Initialize the max upload file size when quotas are enabled

Due to an unwanted check, files causing the quota to be exceeded
were deleted after the upload, but not during the upload.

The bug was introduced in 2009 in version 1.0.23

Spotted by @DroidTest, thanks!
CVE: CVE-2021-40524
CWE: CWE-434
Vulnerability description: In Pure-FTPd before 1.0.50, an incorrect max_filesize quota mechanism in the server allows attackers to upload files of unbounded size, which may lead to denial of service or a server hang. This occurs because a certain greater-than-zero test does not anticipate an initial -1 value. (Versions 1.0.23 through 1.0.49 are affected.)

Project: pure-ftpd
File: ftpd.c

void dostor(char *name, const int append, const int autorename)
{
    ULHandler ulhandler;
    int f;
    const char *ul_name = NULL;
    const char *atomic_file = NULL;
    off_t filesize = (off_t) 0U;
    struct stat st;
    double started = 0.0;
    signed char overwrite = 0;
    int overflow = 0;
    int ret = -1;
    off_t max_filesize = (off_t) -1;
#ifdef QUOTAS
    Quota quota;
#endif
    const char *name2 = NULL;

    if (type < 1 || (type == 1 && restartat > (off_t) 1)) {
        addreply_noformat(503, MSG_NO_ASCII_RESUME);
        goto end;
    }
#ifndef ANON_CAN_RESUME
    if (guest != 0 && anon_noupload != 0) {
        addreply_noformat(550, MSG_ANON_CANT_OVERWRITE);
        goto end;
    }
#endif
    if (ul_check_free_space(name, -1.0) == 0) {
        addreply_noformat(552, MSG_NO_DISK_SPACE);
        goto end;
    }
    if (checknamesanity(name, dot_write_ok) != 0) {
        addreply(553, MSG_SANITY_FILE_FAILURE, name);
        goto end;
    }
    if (autorename != 0) {
        no_truncate = 1;
    }
    if (restartat > (off_t) 0 || no_truncate != 0) {
        if ((atomic_file = get_atomic_file(name)) == NULL) {
            addreply(553, MSG_SANITY_FILE_FAILURE, name);
            goto end;
        }
        if (restartat > (off_t) 0 &&
            rename(name, atomic_file) != 0 && errno != ENOENT) {
            error(553, MSG_RENAME_FAILURE);
            atomic_file = NULL;
            goto end;
        }
    }
    if (atomic_file != NULL) {
        ul_name = atomic_file;
    } else {
        ul_name = name;
    }
    if (atomic_file == NULL &&
        (f = open(ul_name, O_WRONLY | O_NOFOLLOW)) != -1) {
        overwrite++;
    } else if ((f = open(ul_name, O_CREAT | O_WRONLY | O_NOFOLLOW,
                         (mode_t) 0777 & ~u_mask)) == -1) {
        error(553, MSG_OPEN_FAILURE2);
        goto end;
    }
    if (fstat(f, &st) < 0) {
        (void) close(f);
        error(553, MSG_STAT_FAILURE2);
        goto end;
    }
    if (!S_ISREG(st.st_mode)) {
        (void) close(f);
        addreply_noformat(550, MSG_NOT_REGULAR_FILE);
        goto end;
    }
    alarm(MAX_SESSION_XFER_IDLE);

    /* Anonymous users *CAN* overwrite 0-bytes files - This is the right behavior */
    if (st.st_size > (off_t) 0) {
#ifndef ANON_CAN_RESUME
        if (guest != 0) {
            addreply_noformat(550, MSG_ANON_CANT_OVERWRITE);
            (void) close(f);
            goto end;
        }
#endif
        if (append != 0) {
            restartat = st.st_size;
        }
    } else {
        restartat = (off_t) 0;
    }
    if (restartat > st.st_size) {
        restartat = st.st_size;
    }
    if (restartat > (off_t) 0 && lseek(f, restartat, SEEK_SET) < (off_t) 0) {
        (void) close(f);
        error(451, "seek");
        goto end;
    }
    if (restartat < st.st_size) {
        if (ftruncate(f, restartat) < 0) {
            (void) close(f);
            error(451, "ftruncate");
            goto end;
        }
#ifdef QUOTAS
        if (restartat != st.st_size) {
            (void) quota_update(NULL, 0LL,
                                (long long) (restartat - st.st_size),
                                &overflow);
        }
#endif
    }
#ifdef QUOTAS
    if (quota_update(&quota, 0LL, 0LL, &overflow) == 0 &&
        (overflow > 0 || quota.files >= user_quota_files ||
         quota.size > user_quota_size ||
         (max_filesize >= (off_t) 0 &&
          (max_filesize = user_quota_size - quota.size) < (off_t) 0))) {
        overflow = 1;
        (void) close(f);
        goto afterquota;
    }
#endif
    opendata();
    if (xferfd == -1) {
        (void) close(f);
        goto end;
    }
    doreply();
# ifdef WITH_TLS
    if (data_protection_level == CPL_PRIVATE) {
        tls_init_data_session(xferfd, passive);
    }
# endif
    state_needs_update = 1;
    setprocessname("pure-ftpd (UPLOAD)");
    filesize = restartat;

#ifdef FTPWHO
    if (shm_data_cur != NULL) {
        const size_t sl = strlen(name);

        ftpwho_lock();
        shm_data_cur->state = FTPWHO_STATE_UPLOAD;
        shm_data_cur->download_total_size = (off_t) 0U;
        shm_data_cur->download_current_size = (off_t) filesize;
        shm_data_cur->restartat = restartat;
        (void) time(&shm_data_cur->xfer_date);
        if (sl < sizeof shm_data_cur->filename) {
            memcpy(shm_data_cur->filename, name, sl);
            shm_data_cur->filename[sl] = 0;
        } else {
            memcpy(shm_data_cur->filename,
                   &name[sl - sizeof shm_data_cur->filename - 1U],
                   sizeof shm_data_cur->filename);
        }
        ftpwho_unlock();
    }
#endif

    /* Here starts the real upload code */

    started = get_usec_time();

    if (ul_init(&ulhandler, clientfd, tls_cnx, xferfd, name, f, tls_data_cnx,
                restartat, type == 1, throttling_bandwidth_ul,
                max_filesize) == 0) {
        ret = ul_send(&ulhandler);
        ul_exit(&ulhandler);
    } else {
        ret = -1;
    }
    (void) close(f);
    closedata();

    /* Here ends the real upload code */

#ifdef SHOW_REAL_DISK_SPACE
    if (FSTATFS(f, &statfsbuf) == 0) {
        double space;

        space = (double) STATFS_BAVAIL(statfsbuf) *
            (double) STATFS_FRSIZE(statfsbuf);
        if (space > 524288.0) {
            addreply(0, MSG_SPACE_FREE_M, space / 1048576.0);
        } else {
            addreply(0, MSG_SPACE_FREE_K, space / 1024.0);
        }
    }
#endif

    uploaded += (unsigned long long) ulhandler.total_uploaded;
    {
        off_t atomic_file_size;
        off_t original_file_size;
        int files_count;

        if (overwrite == 0) {
            files_count = 1;
        } else {
            files_count = 0;
        }
        if (autorename != 0 && restartat == (off_t) 0) {
            if ((atomic_file_size = get_file_size(atomic_file)) < (off_t) 0) {
                goto afterquota;
            }
            if (tryautorename(atomic_file, name, &name2) != 0) {
                error(553, MSG_RENAME_FAILURE);
                goto afterquota;
            } else {
#ifdef QUOTAS
                ul_quota_update(name2 ? name2 : name, 1, atomic_file_size);
#endif
                atomic_file = NULL;
            }
        } else if (atomic_file != NULL) {
            if ((atomic_file_size = get_file_size(atomic_file)) < (off_t) 0) {
                goto afterquota;
            }
            if ((original_file_size = get_file_size(name)) < (off_t) 0 ||
                restartat > original_file_size) {
                original_file_size = restartat;
            }
            if (rename(atomic_file, name) != 0) {
                error(553, MSG_RENAME_FAILURE);
                goto afterquota;
            } else {
#ifdef QUOTAS
                overflow = ul_quota_update
                    (name, files_count, atomic_file_size - original_file_size);
#endif
                atomic_file = NULL;
            }
        } else {
#ifdef QUOTAS
            overflow = ul_quota_update
                (name, files_count, ulhandler.total_uploaded);
#endif
        }
    }
    afterquota:
    if (overflow > 0) {
        addreply(552, MSG_QUOTA_EXCEEDED, name);
    } else {
        if (ret == 0) {
            addreply_noformat(226, MSG_TRANSFER_SUCCESSFUL);
        } else {
            addreply_noformat(451, MSG_ABORTED);
        }
        displayrate(MSG_UPLOADED, ulhandler.total_uploaded, started,
                    name2 ? name2 : name, 1);
    }
    end:
    restartat = (off_t) 0;
    if (atomic_file != NULL) {
        unlink(atomic_file);
        atomic_file = NULL;
    }
}